Generally speaking, diesel engines may be divided into three separate sizes, small, medium, and large. Small engines generally have a power output less than 50 kilowatts (“kW”), while medium sized diesel engines have a power output ranging between 50 and 500 kW. Large diesel engines most often have a power output greater than 500 kW.
Large diesel engines may further be classified as high, medium, and low speed. Typically, high speed large diesel engines operate at greater than 1000 rotations per minute (“RPM”), and have a cylinder displacement less than 20 liters per cylinder. Medium speed large diesel engines, on the other hand, commonly function between 1000 and 400 RPM, and have a cylinder displacement between 20 and 30 liters per cylinder. Low speed large diesel engines will typically operate at less than 400 RPM, and comprise a cylinder displacement greater than 30 liters per cylinder.
Increased exhaust back pressure can have numerous effects on diesel engines, including increased pumping work, reduced intake manifold boost pressure, and turbocharger problems. While increased exhaust back pressure affects the operation of all diesel engines, it especially affects large diesel engines, and particularly medium and low speed large diesel engines. Accordingly, in order to reduce exhaust back pressure, aftertreatment systems for medium and low speed large diesel engines are designed with an enclosure with a large volume and cross-sectional area, and a larger volume of selective catalytic reduction (“SCR”) catalyst bed. However, increasing the volume of the enclosure and cross-sectional area, and the volume of the SCR catalyst bed, also decreases flow uniformity of the exhaust gases through the SCR catalyst bed, thereby decreasing the effectiveness of the aftertreatment system. Accordingly, a need exists for an aftertreatment system for a medium and low speed large diesel engine having increased flow uniformity.
US Patent Application 2013/0098002 to Danckert at al. (“Danckert”) discloses an exhaust gas treatment device for off-road applications. More specifically, Danckert discloses a SCR system including a circularly shaped canister through which a diffuser tube is positioned in an antechamber. This is followed by a single honeycomb styled mixer and then a hydrolysis catalytic convertor is positioned just upstream of two SCR catalyst beds. While arguably effective for its specific purpose, Danckert only discloses this particular arrangement, and fails to disclose how it would be applied to medium and low speed large diesel engines to increase flow uniformity.
The present disclosure is directed to overcoming one or more problems set forth above and/or other problems associated with the prior art.